546124 Ethene Dimerization over Zr-Based Metal-Organic Framework (UiO-67) Functionalized with Ni and Bipyridine

Wednesday, June 5, 2019
Texas Ballroom Prefunction Area (Grand Hyatt San Antonio)
Mustafa Komurcu, Andrea Lazzarini, Gurpreet Kaur, Silvia Bordiga, Karl Petter Lillerud and Unni Olsbye, Department of Chemistry, University of Oslo, OSLO, Norway

Ethene dimerization over Zr-based metal-organic framework (UiO-67) functionalized with Ni and bipyridine

Mustafa Kømurcu1, Andrea Lazzarini1, Gurpreet Kaur1, Silvia Bordiga1,2, Karl Petter Lillerud, Unni Olsbye1*

1 – Department of Chemistry, University of Oslo, P.O. Box 1033, Oslo 0315, Norway 

2 – Univerisity of Turin, Department of Chemistry, Via P. Giuria 7, Turin 10125, Italy

* corresponding author: Unni.olsbye@kjemi.uio.no


The industrial transition from naphta to ethane as feedstock for ethene production has inspired the search for alternative production processes for propene, butene and butadiene. Dimerization of ethene to linear α-butene is one of a few large-scale homogeneously catalyzed reactions [1]. With the intention of making the process more practical and sustainable, recent research efforts have focused on the development of heterogeneous dimerization catalysts. Ni-aluminosilicates is one promising alternative, and recently, metal-organic framework (MOF) based selective oligomerization catalysts are appearing [2, 3]. An important upside of Ni-aluminosilicate catalysts compared to the traditional homogeneous Ni-complexes is that they do not require a co-catalyst (Et2AlCl). Most Ni-MOF catalysts published to date, however, do require such a co-catalyst [4-6]. Our target is to develop a MOF-based ethene oligomerisation catalyst that does not require a co-catalyst and maintains high linear butene selectivity. In this contribution, we report a series of UiO-67 Zr-MOFs where part of the biphenyl linkers were replaced by bipyridine, as grafting sites for Ni salts. Butene yields up to 1850 mg gcat-1 h-1 were obtained without the use of a co-catalyst. Detailed characterization of fresh and used catalyst was performed to identify the active site and to confirm the structural stability of the catalyst under reaction conditions.

UiO-67, UiO-67-bpy7% and UiO-67-bpy12% (bpy = 2,2’bipyridine-5,5’-dicarboxylate) were functionalized with Ni2+ and characterized by XRD, SEM, N2-adsorption, TEM, UV-VIS and FT-IR. The catalysts were tested as ethene dimerization catalysts in the temperature range from  120 °C - 300 °C, ethene partial pressure from 4 to 26 bar where C.T. = 3.1 mgcatmin mLethene-1. High temperatures (> 200 °C) and ethene partial pressure (> 4 bar) was required to obtain significant conversion. Only catalysts with high concentration of Ni and bpy showed significant activity, with linear butenes as main product. An initial increase in ethene conversion with time on stream was observed, suggesting that the active state of the catalyst is formed during reaction. The catalysts deactivated over the course of the experiments, most likely due to long chain alkenes retained in the structure or due to formation of nickel nanoparticles. Catalytic activity increased with activation time, where longer duration at elevated temperature led to a higher conversion and faster achievement of maximum conversion. TEM images and FTIR measurements showed the presence of Ni/NiO nanoparticles on spent catalyst. Ex-situ CO-FTIR measurements on 2% Ni- UiO-67-bpy12% and 4% Ni- UiO-67-bpy12% used for 0, 100 and 700 min TOS showed that Ni/NiO nanoparticles formed only on 4% Ni- UiO-67-bpy12% after 700 min TOS (Figure 1), eliminating the possibility of nanoparticles as the single active site for the reaction. Ni2+ grafted on bpy linkers is suggested as the active site for this reaction. Switching the feed to 1-butene, no isomerization activity was observed over the bpy-UiO-67. Considering the lack of strong acid sites and taking the product distribution into account we suggest that the catalyst operates through the Cossee-Arlman mechanism.

Figure 1: Left: Ethene conversion (solid symbols) and linear butene selectivity (hollow symbols) at 250 °C for the catalysts (shown in legend) versus time on stream. Reaction conditions: mcat = 0.100 g, 30 bar total pressure where Pethene = 26 bar and Pinert = 4 bar, contact time: 3.1 mg∙min/mL at STP. Right: FT-IR spectra of sample 2% Ni-UiO-67-bpy (blue curve) and 4% Ni-UiO-67-bpy (red curve) collected at the end of reaction. It is possible to notice the v(C-H) from retained products in the 3000 – 2800 cm-1 region. Inset shows the subtracted spectra in the CO spectral region after its adsorption at 77K. The signal at 2170 cm-1 evidence the difference in Ni amount present in the two samples, while the broad peak centered at 2060 cm-1 for 4% Ni-UiO-67-bpy is ascribed to CO coordinated on Ni/NiO NPs.

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